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Note: These instructions seem to be targeted towards people creating a JIT. My compiler compiles to native. I suppose I just need a reference to the stack location of the stack map, wherever that is.</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> llvm-dev <llvm-dev-bounces@lists.llvm.org> on behalf of Jordan Rudd via llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Sent:</b> Thursday, November 1, 2018 2:06 PM<br>
<b>To:</b> llvm-dev@lists.llvm.org<br>
<b>Subject:</b> [llvm-dev] Building GC on statepoint-example</font>
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Hi,</div>
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I'm trying to build a gc using the statepoint-example strategy. However, after hours of searching, reading documentation and trying to find code examples online, I cannot figure out how to access the Stack Map.</div>
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The documentation for statepoint-example says:</div>
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<i><span style="font-family:"Lucida Grande","Lucida Sans Unicode",Geneva,Verdana,sans-serif; font-size:14px; text-align:left; background-color:rgb(255,255,255); display:inline!important">The stack map format generated by this GC strategy can be found in the<span> </span></span><a href="https://nam03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fllvm.org%2Fdocs%2FStackMaps.html%23stackmap-section&data=02%7C01%7C%7Ce9642625652f4a29fc1f08d6403dfa73%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636767032264647521&sdata=2cqSbyrmgxWfRh95yvOnwU6v42J1HRxI7dPwkSLARTY%3D&reserved=0" originalsrc="https://llvm.org/docs/StackMaps.html#stackmap-section" shash="VEGTjfCHpcYeYznX8jdBUdLzAI7QOw6YKFpYgAzyx96kYQZjAGC50JFOdpYfGrMHCl8ppZ1/gmJn7y7VXBPQ03pAaxsXlXodGEgbavdDWyifzHwSRgpZ5fgVpTch3aJlgiU8jQ6h3A/Y0cmyByKynLbBpY1fKjW/41sl5E9JjAg=" style="color:rgb(202,121,0); text-decoration:underline; font-family:"Lucida Grande","Lucida Sans Unicode",Geneva,Verdana,sans-serif; font-size:14px; text-align:left; background-color:rgb(255,255,255)"><span>Stack
Map Section</span></a><span style="font-family:"Lucida Grande","Lucida Sans Unicode",Geneva,Verdana,sans-serif; font-size:14px; text-align:left; background-color:rgb(255,255,255); display:inline!important"><span> </span>using a format documented<span> </span></span><a href="https://nam03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fllvm.org%2Fdocs%2FStatepoints.html%23statepoint-stackmap-format&data=02%7C01%7C%7Ce9642625652f4a29fc1f08d6403dfa73%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636767032264647521&sdata=FhoqamuJExS4ZPyk4i2xnHkGS6A13f0v4wIszJ5oBRE%3D&reserved=0" originalsrc="https://llvm.org/docs/Statepoints.html#statepoint-stackmap-format" shash="fPdsayL0G00r1X/ig1NNrVkyejjKWBfw1LvIRhzBdrbBYC3fMYoUz0QhztdzjGXtFkT773DEJ1+ppgqqWQVSTOe7kfuvH/9EwT5PMWqqPQi2K3OkAwx/8J+5xl7Lkm0QOUByMsKY88BcnIKAQ9zL+FIRyhzyiUFzxkzUIeKRW88=" style="color:rgb(202,121,0); text-decoration:underline; font-family:"Lucida Grande","Lucida Sans Unicode",Geneva,Verdana,sans-serif; font-size:14px; text-align:left; background-color:rgb(255,255,255)"><span>here</span></a><span style="font-family:"Lucida Grande","Lucida Sans Unicode",Geneva,Verdana,sans-serif; font-size:14px; text-align:left; background-color:rgb(255,255,255); display:inline!important">.
This format is intended to be the standard format supported by LLVM going forward.</span></i><br>
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<span style="font-family:"Lucida Grande","Lucida Sans Unicode",Geneva,Verdana,sans-serif; font-size:14px; text-align:left; background-color:rgb(255,255,255); display:inline!important"><br>
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<span style="font-family:"Lucida Grande","Lucida Sans Unicode",Geneva,Verdana,sans-serif; font-size:14px; text-align:left; background-color:rgb(255,255,255); display:inline!important">Ok, great, I see the format. But... how do I access the Stack Map from my
runtime? Where is it? </span></div>
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<span style="font-family:"Lucida Grande","Lucida Sans Unicode",Geneva,Verdana,sans-serif; font-size:14px; text-align:left; background-color:rgb(255,255,255); display:inline!important">The link seems to send me to this instruction:</span></div>
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<span style="font-family:"Lucida Grande","Lucida Sans Unicode",Geneva,Verdana,sans-serif; font-size:14px; text-align:left; background-color:rgb(255,255,255); display:inline!important"><i><span style="font-size:14px; background-color:rgb(255,255,255); display:inline!important">A
JIT compiler can easily access this section by providing its own memory manager via the LLVM C API</span><code style="font-family:Consolas,"Deja Vu Sans Mono","Bitstream Vera Sans Mono",monospace; font-size:0.95em; background-color:rgb(255,255,255)"><span style="">LLVMCreateSimpleMCJITMemoryManager()</span></code><span style="font-size:14px; background-color:rgb(255,255,255); display:inline!important">.
When creating the memory manager, the JIT provides a callback:</span><code style="font-family:Consolas,"Deja Vu Sans Mono","Bitstream Vera Sans Mono",monospace; font-size:0.95em; background-color:rgb(255,255,255)"><span style="">LLVMMemoryManagerAllocateDataSectionCallback()</span></code><span style="font-size:14px; background-color:rgb(255,255,255); display:inline!important">.
When LLVM creates this section, it invokes the callback and passes the section name.</span></i><br>
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<span style="font-family:"Lucida Grande","Lucida Sans Unicode",Geneva,Verdana,sans-serif; font-size:14px; text-align:left; background-color:rgb(255,255,255); display:inline!important"><span style="font-size:14px; background-color:rgb(255,255,255); display:inline!important"><br>
</span></span></div>
<div style="color:rgb(0,0,0)"><font face="Lucida Grande, Lucida Sans Unicode, Geneva, Verdana, sans-serif"><span style="font-size:14px">None of these API's are well-documented, so I'm kind of trying to guess what to do here. As a proof of concept, I tried building
a do-nothing memory manager that calls APILLVMCreateSimpleMCJITMemoryManager on static initialization and passes the callbacks to it. I link the necessary llvm libs into my runtime and fire it up.<br>
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I can confirm that my safepoint poll code is getting hit. I can confirm that creating the "memory manager" is called on runtime boot and that it's succeeding. But the callbacks never get hit. Even if they were, it's unclear how I would use the parameters of
those callbacks to locate the stack map.</span></font></div>
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<div style="color:rgb(0,0,0)"><font face="Lucida Grande, Lucida Sans Unicode, Geneva, Verdana, sans-serif"><span style="font-size:14px">What am I missing? </span></font></div>
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<div style="color:rgb(0,0,0)"><font face="Lucida Grande, Lucida Sans Unicode, Geneva, Verdana, sans-serif"><span style="font-size:14px">Thanks!</span></font></div>
<div style="color:rgb(0,0,0)"><font face="Lucida Grande, Lucida Sans Unicode, Geneva, Verdana, sans-serif"><span style="font-size:14px">Jordan</span></font></div>
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